Financially stricken Parma went into Saturday's clash at the Stadio Ennio Tardini 13 points adrift of safety following a campaign that will be remembered for their off-the-field problems rather than any exploits on the pitch.
But Roberto Donadoni's men managed to give their suffering fans a stunning victory that they could not have envisaged courtesy of a determined performance against the runaway leaders, who are 14 points clear at the top of the table.
Juve dictated play for long periods and created the better the opportunities in the opening 45 minutes, but Parma goalkeeper Antonio Mirante kept them at bay.
With Tuesday's UEFA Champions League quarter-final clash against Monaco perhaps playing on their minds, a Juve side without the services of Carlos Tevez and Andrea Pirlo slumped to their first Serie A defeat since losing to Genoa over five months ago.
Mauri's cool finish from the edge of the area on the hour mark sealed a memorable fifth league win of the season for Parma and their second this week after beating Udinese on Wednesday.
It took 20 minutes for Juve to carve out their first opportunity, Roberto Pereyra's low curling effort turned past the post by Mirante before Ishak Belfodil bent an effort wide at the other end.
The best chance of a disappointing first half came in the 32nd minute when Arturo Vidal met Claudio Marchisio's free-kick, only for Mirante to deny him with a fine far post save from the midfielder's header.
Forward Kingsley Coman then forced the impressive Mirante into action again after finding half a yard of space in the box as Juve finished the first half on the front foot.
But the game became more open upon the restart, and Mauri took advantage by firing Parma into a shock lead.
The midfielder raced on to a lay off from Belfodil on the edge of area and coolly angled the ball into the top-right corner beyond the helpless Marco Storari.
Juve, despite their obvious superior quality, showed little signs of mounting a comeback in the closing stages, with the leaders' forward line frustrated by a determined Parma side.
Parma had little difficulty in holding firm for three points in another defiant display despite their uncertain future.
